Coral reefs have suffered more damage since the 1970s than any time in the last 220,000 years, according to a study that warns of the threats of overfishing and coastal development.

Scientists from Australia have found that coral reefs in the Caribbean island of Barbados were relatively unchanged for about 100,000 years before the arrival of humans, despite rising and falling sea levels.

But according to the paper published in Ecology Letters, modern day reefs now look startlingly different and are dominated by algae and seaweed.

"When you compare that typical coral community in the geological past to the coral community that we see today in Barbados it's fundamentally different," says Pandolfi, who led the study.

"It's clear that these modern coral reefs have been significantly altered and the only thing that's different is that humans are around.

"We see that the impact of overfishing and coastal development has had a huge effect the likes of which we haven't seen for hundreds of thousands of years."

Overfishing takes its toll

Pandolfi studied the preserved remains of entire coral reef communities that lived in the Caribbean up to 220,000 years ago.

He analysed four periods in the reef's history, when geological activity pushed it to the surface and wiped out the coral community.

Each time, the sea floor was recolonised and the coral reef returned in a very similar structure with the same species.

"When we look at large scale perturbations in the fossil record, [such as] global climate change and sea level changes, when the reefs come back .... they appear to assemble in similar ways," he says.

"So through out the last couple of 100,000 years we've had coral reefs in the island of Barbados that are very much alike through time."

But since the 1970s the Elkhorn coral that once dominated the reef has virtually disappeared and algae and seaweed have taken over, he says.

Overfishing is partly to blame, as there are no longer enough large fish and turtles to eat the algae.

"The organisms that eat plants or seaweed or algae have been really hammered by overfishing," Pandolfi says.

"The problem is that the macro-algae compete with the coral for space in the reef and ... because there's no herbivores to keep the seaweed populations in check they're able to take over and the corals can't get back in."

Coastal development, including the destruction of forests for sugar cane and other agriculture, has also impacted on the reef as increased levels of nutrients in the water favour the algae, he says.

"This study is a warning bell that if Australia is not proactive in its coral reef management we will see similar changes in the Great Barrier Reef," Pandolfi says.

"If our reefs are going to survive the impacts of climate change, they have to be at the peak of their health."

Pandolfi says the damage to coral reefs will have an impact on nations that depend on them for food and natural protection from storms.

But he says the changes may be reversible if populations of seaweed and algae-eating herbivores, such as turtles and dugongs, are restored.